The national "yellow alert", issued late on Thursday, comes after regions from Sichuan in the southwest to Shanghai in the Yangtze delta have experienced weeks of extreme heat, with government officials repeatedly citing global climate change as the cause.
In one of the Yangtze's important flood basins in central China's Jiangxi province, the Poyang Lake has shrunk to a quarter of its normal size for this time of year, state news agency Xinhua said.
As many as 66 rivers across 34 counties in the southwestern region of Chongqing have dried up, state broadcaster CCTV said on Friday.
Rainfall in Chongqing this year is down 60 per cent compared with the seasonal norm, and the soil in several districts is severely short of moisture, CCTV said.
The district of Beibei, north of Chongqing's urban centre, saw temperatures hit 45C on Thursday, according to China's weather bureau.
Chongqing accounted for six of the 10 hottest locations in the country on Friday morning, with temperatures in the district of Bishan already approaching 39C. Shanghai was already at 37C.
The Chongqing region's infrastructure and emergency services have come under increasing strain, with firefighters on high alert as mountain and forest blazes erupted across the region.
The gas utility in the district of Fuling also told customers on Friday they would cut off supplies until further notice as they dealt with "serious safety hazards".
The Chongqing agricultural bureau has set up expert teams to protect vulnerable crops and expand planting to compensate for losses ahead of the autumn harvest.
The water resources ministry has instructed drought-hit agricultural regions to draw up rotas determining who can access supplies at any particular time, to ensure they do not run out.
According to data from China's emergency ministry, high temperatures in July alone caused direct economic losses of 2.73 billion yuan ($A580 million), affecting 5.5 million people.
China's National Meteorological Centre renewed its high-temperature red alert on Friday, the 30th consecutive day it has issued alerts.
Forecasters predict the current heatwave will start to abate on August 26.
